In conventional or “wet” lithographic printing, ink receptive regions, known as image areas, are generated on a hydrophilic surface. When the surface is moistened with water and ink is applied, the hydrophilic regions retain the water and repel the ink, and the ink receptive regions accept the ink and repel the water. The ink is transferred to the surface of a material upon which the image is to be reproduced. For example, the ink can be first transferred to an intermediate blanket that in turn is used to transfer the ink to the surface of the material upon which the image is to be reproduced.
Imageable elements useful to prepare lithographic printing plates typically comprise one or more imageable layers applied over the hydrophilic surface of a substrate. The imageable layer includes one or more radiation-sensitive components that can be dispersed in a suitable binder. Alternatively, the radiation-sensitive component can also be the binder material. Following imaging, either the imaged regions or the non-imaged regions of the imageable layer are removed by a suitable developer, revealing the underlying hydrophilic surface of the substrate. If the imaged regions are removed, the element is considered as positive-working. Conversely, if the non-imaged regions are removed, the element is considered as negative-working. In each instance, the regions of the imageable layer (that is, the image areas) that remain are ink-receptive, and the regions of the hydrophilic surface revealed by the developing process accept water and aqueous solutions, typically a fountain solution, and repel ink.
Direct digital imaging has become increasingly important in the printing industry. Imageable elements for the preparation of lithographic printing plates have been developed for use with infrared lasers. Thermally imageable, multi-layer positive-working elements are described, for example, in U.S. Pat. No. 6,294,311 (Shimazu et al.), U.S. Pat. No. 6,352,812 (Shimazu et al.), U.S. Pat. No. 6,593,055 (Shimazu et al.), 6,352,811 (Patel et al.), and U.S. Pat. No. 6,528,228 (Savariar-Hauck et al.), and U.S. Patent Application Publication 2004/0067432 A1 (Kitson et al.).
Other positive-working single- and multi-layer imageable elements containing various unique polymeric binders are described in U.S. Pat. No. 7,049,045 (Kitson et al.), U.S. Pat. No. 7,247,418 (Saraiya et al.) and U.S. Pat. No. 7,300,726 (Patel et al.).
Various properties are desired in such positive-working imageable elements, including resistance to chemicals used during printing and long run length. This can sometimes be achieved by baking the imaged and developed element before use in printing. This “post-baking” process can be achieved at various elevated temperatures, generally greater than 150° C. and for up to 10 minutes.
For example, U.S. Pat. No. 6,893,783 (Kitson et al.), U.S. Pat. No. 7,060,415 (Kitson et al.), U.S. Pat. No. 7,186,482 (Kitson et al.), U.S. Pat. No. 7,247,418 (Saraiya et al.), U.S. Pat. No. 7,291,440 (Ray et al.), U.S. Pat. No. 7,300,726 (Patel et al.), and U.S. Pat. No. 7,338,745 (Ray et al.) describe various means for improving post-bakeability as well as resistance to press chemicals, for example by containing certain polymeric binders.
U.S. Pat. No. 6,699,636 (Savariar-Hauck) describes negative-working and positive-working lithographic imageable elements that include a polymeric binder with acidic groups and a separate crosslinking agent that contains oxazoline groups.